U.S. patent number 8,772,927 [Application Number 13/290,824] was granted by the patent office on 2014-07-08 for semiconductor package structures having liquid cooler integrated with first level chip package modules.
This patent grant is currently assigned to International Business Machines Corporation. The grantee listed for this patent is Raschid Jose Bezama, Evan George Colgan, Michael Gaynes, John Harold Magerlein, Kenneth C. Marston, Xiaojin Wei. Invention is credited to Raschid Jose Bezama, Evan George Colgan, Michael Gaynes, John Harold Magerlein, Kenneth C. Marston, Xiaojin Wei.
United States Patent |
8,772,927 |
Bezama , et al. |
July 8, 2014 |
Semiconductor package structures having liquid cooler integrated
with first level chip package modules
Abstract
Semiconductor package structures are provided which are designed
to have liquid coolers integrally packaged with first level chip
modules. In particular, apparatus for integrally packaging a liquid
cooler device within a first level chip package structure include
structures in which a liquid cooler device is thermally coupled
directly to the back side of an integrated circuit chip flip-chip
mounted on flexible chip carrier substrate. The liquid cooler
device is mechanically coupled to the package substrate through a
metallic stiffener structure that is bonded to the flexible package
substrate to provide mechanical rigidity to the flexible package
substrate.
Inventors: |
Bezama; Raschid Jose (Hopewell
Junction, NY), Colgan; Evan George (Yorktown Heights,
NY), Gaynes; Michael (Yorktown Heights, NY), Magerlein;
John Harold (Yorktown Heights, NY), Marston; Kenneth C.
(Hopewell Junction, NY), Wei; Xiaojin (Hopewell Junction,
NY) |
Applicant: |
Name |
City |
State |
Country |
Type |
Bezama; Raschid Jose
Colgan; Evan George
Gaynes; Michael
Magerlein; John Harold
Marston; Kenneth C.
Wei; Xiaojin |
Hopewell Junction
Yorktown Heights
Yorktown Heights
Yorktown Heights
Hopewell Junction
Hopewell Junction |
NY
NY
NY
NY
NY
NY |
US
US
US
US
US
US |
|
|
Assignee: |
International Business Machines
Corporation (Armonk, NY)
|
Family
ID: |
41315393 |
Appl.
No.: |
13/290,824 |
Filed: |
November 7, 2011 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20120049341 A1 |
Mar 1, 2012 |
|
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
12120029 |
May 13, 2008 |
8115303 |
|
|
|
Current U.S.
Class: |
257/719; 257/718;
257/706; 257/707 |
Current CPC
Class: |
H01L
23/3675 (20130101); H01L 23/473 (20130101); H01L
23/49833 (20130101); H01L 2224/32225 (20130101); H01L
2023/4043 (20130101); H01L 23/4985 (20130101); H01L
2224/73253 (20130101); H01L 2924/19105 (20130101); H01L
2924/15311 (20130101); H01L 2023/4087 (20130101); H01L
2224/32245 (20130101); H01L 2224/73204 (20130101); H01L
2924/10253 (20130101); H01L 2224/16225 (20130101); H01L
2924/15311 (20130101); H01L 2224/73204 (20130101); H01L
2224/16225 (20130101); H01L 2224/32225 (20130101); H01L
2924/00 (20130101); H01L 2924/10253 (20130101); H01L
2924/00 (20130101) |
Current International
Class: |
H01L
23/34 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Such; Matthew W
Assistant Examiner: Kalam; Abul
Attorney, Agent or Firm: F. Chau & Associates, LLC
Percello, Esq.; Louis J.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This is a Continuation Application of U.S. application Ser. No.
12/120,029 filed on May 13, 2008, the disclosure of which is herein
incorporated by reference in its entirety.
Claims
What is claimed is:
1. An electronic apparatus, comprising: a flexible chip carrier
substrate having an IC (integrated circuit) chip flip-chip mounted
on a first surface of the flexible chip carrier substrate and an
area array of electrical contacts formed on a second surface of the
flexible chip carrier substrate opposite the first surface; a
metallic cooler device having upper and lower opposing surfaces and
sidewall surfaces, wherein the lower surface of the metallic cooler
device is thermally bonded directly to a backside surface of the IC
chip; and a stiffener member that is bonded to the first surface of
the flexible chip carrier substrate and is configured to provide
mechanical rigidity to the flexible chip carrier substrate, wherein
the metallic cooler device is mechanically coupled to the flexible
chip carrier substrate by the stiffener member, and wherein the
stiffener member comprises: a planar frame portion that lies
substantially flat against the flexible chip carrier substrate; and
a plurality of extended portions that are integrally formed with
the planar frame portion and extend toward the metallic cooler
device and away from the flexible chip carrier substrate at a first
angle, wherein each the plurality of extended portions includes a
bent end portion that is bent with respect to the rest of the
extended portions at a second angle, the bent end portions are in
contact with the sidewall surfaces of the metallic cooler device,
the bent end portions of the plurality of extended portions being
integrally formed with the rest of the extended portions.
2. The apparatus of claim 1, wherein the metallic cooler device is
thermally bonded to the backside of the IC chip using a layer of
mechanically compliant thermally conductive material or adhesive
thermal bonding material.
3. The apparatus of claim 1, wherein the metallic cooler device is
thermally bonded to the backside of the IC chip using a soft solder
bond.
4. The apparatus of claim 1, wherein the planar frame portion of
the stiffener member is adhesively bonded to an outer peripheral
region of the first surface of the carrier substrate.
5. The apparatus of claim 1, wherein the bent end portions of the
extended portions of the stiffener member are bonded to the
sidewall surfaces of the metallic cooler device using an adhesive
bonding material or solder.
6. An electronic apparatus, comprising: a flexible chip carrier
substrate having an IC (integrated circuit) chip flip-chip mounted
on a surface of the flexible chip carrier; a metallic cooler device
having upper and lower opposing surfaces and sidewall surfaces,
wherein the lower surface of the metallic cooler device is
thermally bonded directly to a backside surface of the IC chip; and
a stiffener member that is bonded to the first surface of the
flexible chip carrier substrate and is configured to provide
mechanical rigidity to the flexible carrier substrate, wherein the
metallic cooler device is mechanically coupled to the flexible chip
carrier substrate by the stiffener member, and wherein the
stiffener member comprises: a rectangular planar frame portion that
lies substantially flat against the flexible chip carrier
substrate; and a plurality of extended portions that are integrally
formed with the rectangular planar frame portion and extend toward
the metallic cooler device and away from the flexible chip carrier
substrate at a first angle, wherein each the plurality of extended
portions includes a bent end portion that is bent with respect to
the rest of the extended portions at a second angle, the bent end
portions are in contact with the sidewall surfaces of the metallic
cooler device, the bent end portions of the plurality of extended
portions being integrally formed with the rest of the extended
portions, and wherein the plurality of extended portions are
disposed against the metallic cooler device with a compressive
force such that the metallic cooler device is configured to receive
a downward tension directly from the plurality of extended
portions.
7. The apparatus of claim 6, wherein the metallic cooler device is
thermally bonded to the backside of the IC chip using a layer of
mechanically compliant thermally conductive material or adhesive
thermal bonding material.
8. The apparatus of claim 6, wherein the metallic cooler device is
thermally bonded to the backside of the IC chip using a soft solder
bond.
9. The apparatus of claim 6, wherein the rectangular planar frame
portion of the stiffener member is adhesively bonded to an outer
peripheral region of the surface of the carrier substrate.
10. The apparatus of claim 6, wherein the bent end portions of the
extended portions of the stiffener member are bonded to the
sidewall surfaces of the metallic cooler device using an adhesive
bonding material or solder.
Description
BACKGROUND
1. Technical Field
The present invention relates generally to semiconductor package
structures having liquid coolers integrally packaged with first
level chip modules and, more specifically, apparatus and methods
for integrally packaging a liquid cooler device with in a first
level chip package structure wherein the liquid cooler device is
thermally coupled directly to the back side of an integrated
circuit chip flip-chip mounted on flexible chip carrier substrate,
and wherein the liquid cooler device is mechanically coupled to the
package substrate through a metallic stiffener structure that is
bonded to the flexible package substrate to provide mechanical
rigidity to the flexible package substrate.
2. Discussion of Related Art
Technological innovations in semiconductor fabrication and
packaging technologies have enabled development of high
performance, and high integration density semiconductor chip
modules. As chip geometries are scaled down and operating speeds
are increased and chip packages become more compact, however, power
densities are increased resulting in more heat generation per unit
area. The increased power density poses practical limitations to
the level of integration density and performance that may be
achieved. Indeed, the ability to implement chip modules with higher
densities and higher performance is limited primarily by the
ability to effectively cool the chip modules during normal
operation. For instance, as heat is generated by IC chips during
normal operation, cooling structures must be employed to provide
sufficiently low thermal resistance paths between the chips and
ambient air or a circulating liquid coolant to adequately remove
heat and maintain the operating temperature of the chips low enough
to assure continued reliable operation. In high performance, high
density chip package structures, air cooling solutions are not
capable of removing heat due to very high power density or due to
space and/or air flow limitations, thereby requiring liquid cooling
solutions (e.g., water coolant).
Moreover, effective cooling solutions are important in high
performance, high density package structures to minimize mechanical
stresses that may occur over temperature cycling (caused by power
cycling) due to the differences in thermal expansion between
different components of the chip package structure. More
specifically, package components formed from materials having
different coefficients of thermal expansion (CTE) tend to expand
and contract by different amounts during thermal cycling, which is
a phenomenon known as "CTE mismatch". The CTE represents the ratio
of change in dimensions to original dimensions per degree rise in
temperature, expressed in ppm/.degree. C. CTE mismatch denotes the
difference in the coefficients of thermal expansions of two
materials or components joined together, which produces strains and
stresses at joining interfaces or in attachment surfaces.
By way of example, in conventional packaging technologies, chip
level packages can be constructed with one or more chips mounted on
a thin flexible first level package substrate, such as an organic
laminate build up package substrate, using micro solder bump
connections, referred to as C4's (controlled collapse chip
connection). A key issue with first level organic package
substrates is the CTE mismatch between silicon chips (.about.3
ppm/C) and the composite laminate carrier substrate (15-20 ppm/C)
to which the chips are attached via C4s. Such CTE mismatch can
result in mechanical stresses on the C4 connections between the
chip and the organic carrier substrate during thermal cycling. As
these mechanical stresses are applied over repeated thermal cycles,
the C4 connections may become fatigued and fail. To counteract
stress to C4 connections, underfill materials may be applied
between the chip and carrier to protect the C4 solder bumps.
Moreover, even when underfill material is used to maintain the
structural integrity of C4 contacts, the stress generated by the
CTE mismatch between the silicon chip and organic substrate, for
example, can result in bowing or bending of substrates and chips.
For instance, the differences in thermal expansion between the
silicon chip and the organic carrier substrate can cause the chip
to warp by 60 microns or more after processing, and cause the
substrate to be even more substantially warped. Such bending/bowing
can not only generate significant stresses and strains in the
electrical contacts between the chip and substrate, but the chip
may be subjected to a high tensile stress, so a small defect or
scratch can result in chip cracking or delamination of the organic
substrate layers. This warpage resulting from CTE mismatch between
silicon chip and organic carrier substrate during thermal cycling
becomes worse as the chip size increases and this is particularly
problematic for lidless packages where the backside surface of the
chip is exposed.
To counteract possible warping of package, various types of
mechanical stiffening structures may be employed to provide
mechanical rigidity to flexible package substrates such as polymer
substrates and organic laminate build up package substrates. For
instance, conventional packaging techniques utilize mechanical
stiffener structures, e.g., planar stiffener plates, package lid
structures, and a combination of stiffener plates and package lid
structures, which are bonded to package substrates in ways that
counteract mechanical stresses arising from differential thermal
expansion between chip and substrate, for example, to reduce
flexure during thermal cycling and otherwise improve the overall
structural reliability of the package. Various conventional
semiconductor chip package structures in which mechanical
stiffening structures are used with first level SCM (single chip
module) chip packages to reduce flexure, will be now be discussed
in detail below with reference to FIGS. 1A/B, 2A/B and 3.
FIGS. 1A and 1B schematically illustrate an embodiment of an
electronic module (10) having a conventional framework for
packaging a single chip module (SCM) with a liquid cooling module
onto a circuit board (20). In particular, FIG. 1A is a schematic
side view of an electronic module (10) comprising a circuit board
(20) (PCB, node card, printed wiring board, printed circuit card,
etc.), a 1.sup.st level chip package (30) and cooler device (40) in
a stacked configuration. The chip package (30) generally comprises
an organic laminate package substrate (31) (or "chip carrier"), an
IC (integrated circuit) chip (32), and a package lid (33). The
cooler (40) is mechanically attached to the circuit board (20)
using an attachment device (50). FIG. 1B is a schematic top plan
view of the electronic module (10) along line 1B-1B in FIG. 1A,
excluding the package lid (33), cooler device (40) and attachment
devices (50).
As depicted in FIGS. 1A and 1B, the semiconductor IC chip (32) is
flip-chip mounted to a top-side surface of the chip carrier
substrate (31) using an array of fine pitch solder balls (34) such
as C4 (Controlled Collapsed Chip Connect) solder balls that provide
electrical connections between an array of I/O pads on the active
surface of the chip (32) and a footprint of corresponding I/O pads
on the top-side surface of the chip carrier substrate (31). The IC
chip (32) is mechanically coupled to the organic chip carrier
substrate (31) using an underfill material (35) disposed between
the IC chip (32) and the organic chip carrier (31) encapsulating
the C4 connections (34). The chip (32) is disposed in a central
region of the substrate (31) and surrounded by underfill material
(35) which extends beyond the edge of the chip (32) to form a
fillet. The underfill material (35) (e.g., epoxy) is a rigid
material that serves to redistribute mechanical stresses in the
interface between the chip (32) and the carrier substrate (31)
caused by the CTE mismatch between the chip carrier (31) and the
chip (32), to thereby minimize stress applied to the C4 connections
(34). Other devices such as decoupling capacitors (37) are shown
mounted on the first surface of the chip carrier (31) using micro
solder balls. In FIG. 1B, the decoupling capacitors (37) are shown
to be placed along two opposite sides of the chip (32).
The chip carrier substrate (31) may comprise electrical contacts
formed on the first surface thereof to provide electrical
interconnections between the chip (32) and devices (37) using
wiring inside the substrate (31) (not shown). As depicted in FIG.
1A, an array of larger pitch solder balls (36) provide electrical
connections between an array of contact pads formed on a second
major (bottom) surface of the substrate (31) and a corresponding
array of I/O contacts formed on the top surface of the circuit
board (20), providing an area array connection known as a ball grid
array (BGA). The circuit board (20) includes a plurality of wiring
layers (21) that are connected to one or more plated through holes
(22). The plated through holes (22) provide electrical connections
between the array of I/O contacts on the top surface of the board
(20) with the wiring layers (21) connected to the plated through
holes (22).
In the exemplary framework of FIGS. 1A-B, the package lid (33)
functions as a mechanical stiffener member and a heat spreader. The
package lid (33) includes an outer rim (33a) that surrounds and
defines a lid cavity (33b) region that encloses the integrated
circuit chip (32) and other devices (37) when the package lid (33)
is mounted to the chip carrier (31). The package lid (33) is
attached to the chip carrier (31) by bonding the lid outer rim
(33a) to the outer peripheral surface region of the chip carrier
(31) using a layer of adhesive material (38). In this regard, the
package lid (33) serves as a stiffener member that provides
supports for the chip carrier substrate (31) to counteract
thermal/mechanical stresses and reduce semiconductor package
warpage and improve the overall reliability. The package lid (33)
can be made of copper with a thickness of 0.5 mm to 2.0 mm. The
package lid (33) design can vary depending on the application but
the package lid (33) design is an important consideration in the
overall package framework as a package lid which is too thick and
too stiff can result in excessive stress and failure in the
package.
The package lid (33) also serves as a heat spreader for cooling the
IC chip (32) wherein the package lid (33) extends over the back
surface of the chip (32) wherein the inner surface of the lid
cavity (33b) is thermally coupled to the backside of the chip (32)
using a layer of thermal interface material (TIM) (39). The TIM
layer (39) is typically formed of a mechanically compliant,
thermally conductive material which provides mechanical compliance
and serves as a primary thermal path to transfer heat from the IC
chip (32) to the package lid (33). The package lid (33) is
thermally coupled to the cooling device (40) using a second layer
of TIM (45). The TIM layer (39), package lid (33) and second TIM
layer (45) provide a thermal path for conducting heat from the
backside of the chip (32) to the cooling device (40) where the heat
is dissipated by the cooling device (40) via air or liquid cooling.
In the conventional framework of FIG. 1A, the second TIM layer (45)
would typically consist of a filled paste or grease, or a phase
change material such as a filled wax, which are reworkable, as
opposed to a filled adhesive or gel material which require curing
at 100-150 C and are not easily reworkable. For most TIMs, the
filler material has a high thermal conductivity such as silver,
graphite, or ceramic particles, for example. The first TIM layer
(39) between the chip (32) and the bottom surface of the package
lid (33) would typically be a filled adhesive or gel material as
opposed to a fluid material such as pastes or greases that could be
"pumped out" by the package displacements during thermal cycling.
This would be less of a concern for the second TIM layer (45) when,
for instance, the cooler (40) and package lid (33) are formed of
the same material, e.g., copper, or materials having similar
CTEs
The cooling device (40) may be an air cooled heat sink or a liquid
cooler device having a plurality of thermal fins (41) that define
open channels (42) through which air or liquid may flow to remove
heat from the thermal fins (41). The cooler (40) is mechanically
attached to the mother board (20) using the attachment device (50)
which is configured to apply a compressive load to hold the cooler
(40) against the top surface of the package lid (33). As depicted
in FIG. 1B, a plurality of mounting holes (51) are formed through
the mother board (20) in proximity to each corner of the carrier
substrate (31) for insertably receiving the attachment devices
(50). This attachment scheme uses hardware that requires holes (51)
to be formed in the electrical board (20) which blocks some wiring
channels of the circuit board (20). In this conventional framework,
the SCM chip package (30) would be attached to the circuit board
(20) by a solder reflow process if BGA or CGA electrical
interconnects are used, or plugged into a socket if PGA electrical
interconnects are used, or aligned to an LGA connector if LGA
electrical interconnects are used. The second TIM layer (45) would
then be dispensed onto the lid (33), or the bottom of the cooler
device (40), and they would be joined and the cooler device (40)
secured to the circuit board (20) by the attachment devices (50).
As described above, it would be desirable to use a TIM2 (45)
material which is reworkable and does not require curing at an
elevated temperature.
FIGS. 2A and 2B schematically illustrate another embodiment of an
electronic module having a conventional framework for packaging a
single chip module (SCM) with a cooling module onto a circuit board
(20). In particular, FIG. 2A is a schematic side view of an
electronic module (11) including a printed circuit board (PCB) (20)
(or node card, printed wiring board, or printed circuit card), a
1.sup.st level chip package (60) and cooler device (40) in a
stacked configuration with the chip package (60) interposed between
the circuit board (20) and the cooler device (40). FIG. 2B is a
schematic top plan view of the electronic module (11) along line
2B-2B in FIG. 2A excluding the planar package lid (64), cooler
device (40) and attachment devices (50). Except for the first level
chip package (60), the electronic module (11) illustrated in FIGS.
2A-B has a conventional framework that is similar to that of the
electronic module (10) in FIGS. 1A-1B, and therefore, a detailed
explanation is not required.
The chip level package (60) includes a separate stiffener member
(62) and a planar package lid (64). As shown in FIG. 2A, the
stiffener member (62) is attached to a perimeter region of the
organic laminate chip carrier (31) with a layer of adhesive
material (61) and the planar package lid (64) is attached to the
stiffener member (62) with a layer of adhesive material (63). As
depicted in FIG. 2B, the stiffener member (62) has a rectangular
frame-like structure with an outer border (62a) and inner border
(62b). The outer border (62a) has a rectangular shape that
corresponds to the outer perimeter of the chip carrier substrate
and the inner border (62b) has a rectangular shape that defines an
inner open region which aligns to the inner surface region of the
carrier substrate (31) in the area occupied by the chips (32) and
surrounding devices (37).
As compared to the conventional package structure (10) of FIGS.
1A/1B, the conventional package structure (11) of FIGS. 2A and 2B
can be constructed in a process by which the stiffener member (62)
is attached to the organic carrier (31) prior to the chip mounting
process, which reduces possible warping of the substrate (31) and
maintains the flatness of the substrate (31) before the chip (32)
is attached to the chip carrier substrate (31), and further
provides the requisite mechanical support during a solder reflow
process when the chip (32) is mounted to the chip carrier (31). The
types of adhesive used to form layers (61) and (63) will vary
depending on the desired mechanical properties.
In this conventional framework, the SCM chip package (60) would be
attached to the circuit board (20) by a solder reflow process if
BGA or CGA electrical interconnects are used, or plugged into a
socket if PGA electrical interconnects are used, or aligned to an
LGA connector if LGA electrical interconnects are used. A second
TIM layer (45) would than be dispensed onto the lid (33), or the
bottom of the cooler device (40), and they would be joined and the
cooler device (40) secured to the circuit board (20) by the
attachment devices (50). As described above, it would be desirable
to use a TIM2 (45) material which is reworkable and does not
require curing at an elevated temperature.
FIG. 3 schematically illustrates another embodiment of an
electronic module having a conventional framework for packaging a
single chip module (SCM) with a cooling module onto a circuit board
(20). In particular, FIG. 3 is a schematic side view of an
electronic module (12) including a printed circuit board (PCB) (20)
(or node card, printed wiring board, or printed circuit card), a
1.sup.st level chip package (70) and cooler device (40) in a
stacked configuration with the chip package (70) interposed between
the circuit board (20) and the cooler device (40). The cooler (40)
is mechanically attached to the circuit board (20) using an
attachment device (50). Except for the first level chip package
(70), the electronic module (12) illustrated in FIG. 3 has a
conventional framework with similar components of the electronic
modules (10) and (11) discussed above, and therefore, a detailed
explanation is not required.
With the electronic module (12) of FIG. 3, the chip level package
(70) includes a rectangular shaped stiffener member (72) that is
attached to a perimeter region of the organic laminate chip carrier
(31) with a layer of adhesive material (71), but the chip level
package (70) does not include a package lid structure (as compared
to the chip package (30) with package lid (33) and the chip package
(60) with package lid (64)). The electronic module (12) is a
lidless SCM structure in which the stiffener member (72) may have a
structure similar to the stiffener member (62) depicted in FIG. 2B,
but the thickness of the stiffener member (72) can be varied to
obtain a given stiffness. In the conventional embodiment of FIG. 3,
a heat spreading function is achieved by thermally bonding the
backside of the chip (32) directly to the bottom surface of the
cooler device (40) using a mechanically compliant, thermal
interface layer (TIM) (73).
The conventional package structure (12) of FIG. 3 provides a lower
thermal resistance thermal path between the backside of the chip
(32) and cooler (40), as compared to the conventional lidded SCM
package structures (10) and (11) in which lid structures are
disposed in the thermal path between the chip (32) and cooling
device (40). Indeed, a lower thermal resistance path is achieved by
eliminating the thermal resistance of a package lid between the
chip (32) and cooler (40) and the thermal resistance that exists
due to the TIM2 layer (45) between the package lid and cooler (40).
Indeed, in FIG. 3, the thermal resistance in the path between the
chip (32) and cooler (40) is based on the thickness and material
used to form the TIM layer (73). Although a lidless chip package
structure (12) of FIG. 3 can theoretically provide increased
thermal performance, the ability to actually achieve a low thermal
resistance TIM layer (73) between the chip (32) and cooler (40) in
the framework of FIG. 3 is problematic by virtue of the increased
mechanical complexity of having the cooler (40) attached to the
circuit board (20) and the chip (32) attached to the laminate
carrier (31) which is attached to the board (20).
More specifically, in the framework of FIG. 3, the cooler (40) is
mechanically attached to the circuit board (20) using the
attachment device (50), which would typically apply a compressive
load to hold the cooler (40) in a fixed position against the
backside surface of the chip (32) With this framework, it is
important to obtain and maintain the requisite bond line (i.e.,
desired uniform thickness of TIM (73) between the chip (32) and
cooler (40). Thus, when the cooler (40) is being mounted, it is
important to ensure that the cooler (40) is maintained flat against
the back surface of the chip (32), and that excessive force is not
applied to the chip (32), and that the chip (32) is protected
against excessive forces from shock or vibration so as to obtain
and maintain the requisite bond line of TIM layer (73). The TIM
layer (73) would typically consist of a filled paste or grease, as
it is undesirable to use a filled adhesive or gel materials which
would require curing at 100-150.degree. C. and which are not easily
reworkable. However, the disadvantage of using a paste or grease is
its tendency to pump out from the space between the backside of the
chip (32) and the cooler (40) as a result of thermal excursions
where chip warpages vary due to the mechanical complexity of having
the cooler (40) attached to the board (20) and the chip (32)
attached to the laminate carrier (31) which is attached to the
board (20).
In this conventional framework, the SCM chip package (70) would be
attached to the circuit board (20) by a solder reflow process if
BGA or CGA electrical interconnects are used, or plugged into a
socket if PGA electrical interconnects are used, or aligned to an
LGA connector if LGA electrical interconnects are used. A TIM layer
(73) would then be dispensed onto the back side of the chip (32),
or the bottom of the cooler device (40), and they would be joined
and the cooler device (40) secured to the circuit board (20) by the
attachment devices (50). As described above, it would be desirable
to use a TIM (73) material which is reworkable and does not require
curing at an elevated temperature.
State of the art chip packaging technologies typically utilize
metallic material such as copper to construct chip package cooler
devices (e.g., liquid coolers) or heat sink structures because
copper has a very high thermal conductivity, and can be readily
machined/etched/formed into fine features and dimensions (e.g.,
micro channel cooler devices) with low manufacturing costs.
Typically, copper liquid cooler devices are used for cooling chips
mounted on ceramic multichip modules (MCMs). However, in each of
the conventional frameworks discussed above, the cooler (40) is
physically attached to the circuit board (20), the footprint of the
cooler (40) must be larger than the footprint of the chip (32) and
extend past the outer periphery of the chip (32) so as to connect
to the board (20). This large size metallic cooler posed practical
limitations such as follows:
When a BGA (ball grid array) or CGA (column grid array) attachment
techniques are used to mechanically/electrically connect the
carrier (31) to the circuit board (20), a large size metallic
cooler (40) results in a large thermal mass that is not compatible
with the BGA or CGA reflow process. Moreover, the resulting weight
of the SCM module may be too high preventing the module from
self-aligning to the printed circuit board pads and can compress
the liquid solder excessively thereby causing shorts during the
solder reflow process. Therefore, with a BGA or CGA electrical
interconnect to the circuit board (20) a large size metallic cooler
may need to be attached to the SCM chip package after the reflow
process used to attach the SCM chip package to the circuit board.
For other mechanical area array connection methods such as LGA
(land grid array) or a pin grid array (PGA), where a compressive
force must be applied for actuation, such compressive forces may
result in a thin and/or non uniform thickness of the TIM layer
between the liquid cooler and chip.
In this regard, when designing chip packages, various factors must
be considered, such as carrier structure, types of package
materials and underfill used, the fabrication process flow, chip
size, thermal properties, etc., to minimize or prevent package
defect mechanisms and structural failures as a result of strains
and stresses that may arise from thermal cycling during production,
joining processing, and use.
BRIEF SUMMARY
Exemplary embodiments of the invention generally include
semiconductor package structures having liquid coolers integrally
packaged with first level chip modules and, more specifically,
apparatus and methods for integrally packaging a liquid cooler
device within a first level chip package structure wherein the
liquid cooler device is thermally coupled directly to the back side
of an integrated circuit chip flip-chip mounted on flexible chip
carrier substrate, and wherein the liquid cooler device is
mechanically coupled to the package substrate through a metallic
stiffener structure that is bonded to the flexible package
substrate to provide mechanical rigidity to the flexible package
substrate. Exemplary embodiments of the invention include a variety
of structures for integrating a metallic liquid cooling device with
a metallic stiffener and/or lid for a high power IC chip mounted
active side down on an organic carrier to form first level package
structures that can be subsequently attached to a printed wiring
board using an array of solder balls, an array of solder columns, a
land grid array, or a pin grid array.
For example, in one exemplary embodiment of the invention, a
metallic cooler device is integrated into a first level chip
package module using a metallic stiffener member having a planar
frame portion that is adhesively bonded to an outer peripheral
region of the first surface of the carrier substrate, and extension
tabs that extend from the planar frame portion towards the metallic
cooler, wherein the extension tabs are coupled to the metallic
cooler device to provide a mechanical attachment for the metallic
cooler device. The stiffener extensions provide a mechanical
attachment for the cooler and/or a controlled compressive force
between the cooler and the chip mounted on the carrier.
In other exemplary embodiments of the invention, metallic coolers
are designed with extensions that overlap and are adhesively
attached to a stiffener or extensions which are adhesively attached
directly to the top surface of the organic carrier. In other
exemplary embodiments, the edges of the cooler are joined to an
opening which is formed in the package lid where the lid is either
attached to a stiffener which is attached to the carrier, or the
lid is attached directly to the carrier. In a preferred embodiment,
the active region of the cooler is smaller than the area of the
chip, but including the seal regions and manifold regions, the
cooler is equal in size, or extends beyond the chip.
These and other exemplary embodiments, aspects, features, and
advantages of the present invention will become apparent from the
following detailed description of exemplary embodiments, which is
to be read in connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
FIGS. 1A and 1B schematically illustrate an embodiment of an
electronic module having a conventional framework for packaging a
single chip module (SCM) with a liquid cooling device.
FIGS. 2A and 2B schematically illustrate another embodiment of an
electronic module having a conventional framework for packaging a
single chip module (SCM) with a cooling device.
FIG. 3 schematically illustrates another embodiment of an
electronic module having a conventional framework for packaging a
single chip module (SCM) with a cooling device.
FIGS. 4A and 4B schematically illustrate an electronic module
having a chip level package structure with an integrated cooler,
according to an exemplary embodiment of the invention.
FIG. 5 schematically illustrates an electronic module having a chip
level package structure with an integrated cooler, according to
another exemplary embodiment of the invention.
FIG. 6 schematically illustrates an electronic module having a chip
level package structure with an integrated cooler, according to
another exemplary embodiment of the invention.
FIG. 7 schematically illustrates an electronic module having a chip
level package structure with an integrated cooler, according to
another exemplary embodiment of the invention.
FIG. 8 schematically illustrates an electronic module having a chip
level package structure with an integrated cooler, according to
another exemplary embodiment of the invention.
FIG. 9 schematically illustrates an electronic module having a chip
level package structure with an integrated cooler, according to
another exemplary embodiment of the invention.
FIGS. 10A and 10B schematically illustrate an electronic module
having a chip level package structure with an integrated cooler,
according to another exemplary embodiment of the invention.
FIG. 11 schematically illustrates an electronic module having a
chip level package structure with an integrated cooler, according
to another exemplary embodiment of the invention.
FIGS. 12A and 12B schematically illustrate an exemplary embodiment
of a metallic cooler device that may be implemented in any of
exemplary embodiments of the invention.
FIG. 13 schematically illustrates an exemplary cooler device that
is thermally bonded to the backside of the chip using a TIM layer
where the cooler is sized such that the cooler width is similar to
the width of the chip and where the sides of the cooler do not
extend past the sides of the chip, according to an exemplary
embodiment of the invention.
FIG. 14 schematically illustrates an exemplary cooler device that
is thermally bonded to the backside of the chip using a TIM layer
where the cooler is sized such that the cooler width is larger than
the width of the chip at least in one dimension, according to an
exemplary embodiment of the invention.
FIGS. 15A.about.15D are exemplary graphical diagrams that
illustrate results of thermal modeling with respect to total
thermal resistance (Rtotal) versus active cooler width WAA (in mm)
for various seal band widths with different fixed base thickness
values.
DETAILED DESCRIPTION
Various techniques for constructing electronic modules having chip
level package structures with integrally packaged metallic liquid
cooling devices will now be described in further detail with
reference to exemplary embodiments discussed hereafter. In general,
electronic apparatus according to exemplary embodiments of the
invention include semiconductor chip modules, such as SCMs, having
an IC chip flip chip mounted on a first (top side) surface of a
flexible carrier substrate having an area array of electrical
contacts formed on a second (bottom side) surface of the substrate
opposite the first surface, a metallic cooler thermally coupled
directly to a backside surface of the IC chip and a stiffener
member which is (i) bonded to the first surface of the carrier
substrate to provide mechanical rigidity to the carrier substrate,
as well as (ii) mechanically coupled to the metallic cooler to
fixedly dispose the metallic cooler device in place on the backside
of the IC chip.
The maturity of organic laminate substrate technology has rapidly
increased while the unit cost has decreased, and it is now the
preferred 1.sup.st level packaging technology for high performance
chip carriers. A typical organic carrier substrate consists of
multiple core layers, typically with sequentially built up
fine-pitch wiring layers on top and bottom surfaces, with a total
thickness of about 0.8 mm or less. In the future, to support finer
via pitches and line widths, the total thickness will be reduced to
0.5 mm and perhaps even to 0.3 mm. This reduction in thickness will
greatly reduce the stiffness and mechanical strength of the organic
carrier substrate, resulting in them being even more flexible.
Exemplary embodiments of the invention as discussed herein below
allow for integration of metallic liquid cooler devices in first
level chip packages where chips are mounted face down on thin
organic substrates.
FIGS. 4A and 4B schematically illustrate an electronic module
having a chip level package structure with an integrated cooler,
according to an exemplary embodiment of the invention. In
particular, FIGS. 4A and 4B are schematic views of an electronic
module (100) comprising a circuit board (110) (e.g., PCB, node
card, printed wiring board, printed circuit card, etc,) and a chip
package structure (120) mounted on the circuit board (110). FIG. 4A
is a schematic side view of the electronic module (100) taken along
line 4A-4A in FIG. 4B, and FIG. 4B is a top plan view of the
electronic module (100) along line 4B-4B in FIG. 4A. As shown
in
FIG. 4A, the chip package structure (120) may be a first level chip
package structure comprising a first level chip carrier (121)
(package substrate), an IC (integrated circuit) chip (122), a
cooler device (123) stacked on the backside of the IC chip (122)
and a metallic stiffener member (130). In general, the package
substrate (121) is a flexible substrate, such as a polymer
substrate or organic build-up laminate substrate, etc., which is
electrically and mechanically coupled to the the circuit board
(110) using an area array of electrical contacts (124) such as BGA
electrical contacts, although other area array connection
techniques may be used to mechanically and electrically couple the
chip package structure (120) to the circuit board (110), such as
CGA, PGA or LGA connections. The circuit board (110) comprises
various levels of wiring (111) and a plurality of plated through
holes (112) that are electrically connected to the contacts
(124).
The IC chip (122) is flip-chip mounted to the top surface of the
chip carrier (121) using an area array of C4 solder ball
connections (125) and an underfill material (126) (e.g., epoxy)
that encapsulates the C4 contacts (125) and bonds the chip (122) to
the carrier (121). The metallic liquid cooling module (123) (or
cooling apparatus) is thermally coupled directly to the non-active
surface of the IC chip (122) using a TIM1 layer (127) and fixedly
disposed on the non-active surface of the IC chip (122) using a
stiffener member (130). As explained hereafter, the stiffener
member (130) serves a dual function of providing mechanical
rigidity to the flexible substrate (121) and mechanically coupling
the cooler device (123) to fixedly hold or otherwise clamp the
cooler device (123) in place on the backside of the chip (122) for
purposes of integrating the cooler (123) into the 1.sup.st level
chip package.
As illustrated in FIGS. 4A and 4B, the stiffener member (130)
comprises a planar frame portion (131) and a plurality of extended
portions (132) (alternatively referred to as "extension tabs"). The
planar frame portion (131) is an outer frame structure that is
bonded to the peripheral surface region of the substrate (121) via
a layer of adhesive (133) (e.g., a flexible adhesive material such
as 3M 1509 or a much stiffer adhesive such as Pyralux). The
extension tabs (132) extend from the frame portion (131) and have
bent end portions (132a) that are bonded to the sidewalls of the
cooler (123) with a layer of adhesive (134) or joining material
such as a solder. As readily illustrated in FIG. 4B, the frame
portion (131) of the metallic stiffener member (130) comprises a
continuous, planar rectangular-shaped frame structure with an outer
border (131a) and an inner border (131b), which is sized and shaped
to bond to the peripheral surface region of the chip carrier (121).
The outer border (131a) has a rectangular shape that corresponds to
the outer perimeter of the chip carrier substrate (121) and the
inner border (131b) has a rectangular shape that defines an inner
open region which aligns to the inner surface region of the carrier
substrate (121) in the area occupied by the chip (122) and
surrounding devices (128). The extension tabs (132) are arranged on
each side of the cooler device (123) and extend from each side of
the inner rectangular border (131b) of the planar frame (131) with
the extension tabs (132) bonded to the sidewalls of the cooler
(123). The cooler device (123) includes coolant fluid inlet and
outlet ports P1, P2 on the top surface of the cooler (123).
In the exemplary embodiment of FIG. 4B, the stiffener extension
tabs (132) are not continuous but have openings aligned to and
exposing regions of the substrate (121) on which decoupling
capacitors (128) are mounted. In particular, in FIG. 4B, the
extension tabs (130) on each side of the cooler (123) include three
separate tabs that are commonly connected at the ends thereof,
i.e., one end of the tabs are commonly connected to the planar
frame portion (131) and other ends of the tabs are connected to a
single bent end portion (132a) which is coupled to the sidewall of
the cooler device (123). In another embodiment, each extension tab
(132) that extends from the inner border (131b) on each side of the
cooler (123) may be one continuous tab structure that extends over
the top of any decoupling capacitors (128) or other components,
with no openings.
It is to be appreciated that extension tabs (132) can be fabricated
as part of the stiffener (130) and integrally formed with the frame
portion (131). The stiffener member (130) with extension tabs (132)
can be formed from stamping a thin planar metallic material such as
copper or aluminum to form a planar metallic pattern of the frame
and tabs, followed by a secondary operation to physically bend
portions of the resulting stiffener into a desired shape, or the
modified stiffener could perhaps be fabricated in a single stamping
or coining operation. It is to be appreciated that stiffener
structures with extension tabs can be designed with varying shapes
and dimensions to provide varying degrees of mechanical coupling
and stiffness between the portion of the stiffener attached to the
perimeter of the carrier and the cooler mounted over the chip to
flatten the carrier, reduce the stress in the chip due to the
thermal expansion mismatch between the carrier and chip, and
improve the reliability by reducing the total flexure during
thermal cycling. For example, the stiffener extension tabs can be
formed with ridges, bends, and/or creases to achieve certain
mechanical properties that provide necessary mechanical forces for
fixedly maintaining the cooler device in position on the backside
surface of the chip.
In FIG. 4A, the stiffener member (130) has extension tabs (132)
that are designed to fixedly clamp the cooler (123) in position
over the backside of the chip (122). In other exemplary embodiments
of the invention, the extension tabs (132) can be shaped to not
only fixedly clamp the cooler (123) in position over the backside
of the chip (122), but also shaped to be in tension to apply a
downward force to hold the cooler (123) against the back surface of
the chip (121). For example, FIGS. 5 and 6 schematically illustrate
electronic modules having chip level packages with integrated
cooler modules according to other exemplary embodiments of the
invention. In particular, FIGS. 5 and 6 are schematic side views of
respective electronic modules (101) and (102) that are similar in
design to the electronic module (100) of FIG. 4A except for
differences in shapes and configurations of stiffener members.
In FIG. 5, a stiffener member (130') includes a planar frame
portion (131) and extension tabs (132) that are shaped to not only
fixedly clamp the cooler (123) in position over the backside of the
chip (122), but also shaped to be in tension to apply a downward
force to hold the cooler (123) against the back surface of the chip
(122) in FIG. 5, the extension tab (132) includes a plurality of
bent portions (132a), (132b) and (132c), with the end portion
(132a) fixedly bonded to the sidewalls of the cooler (123). In this
framework, the bent portions (132b) and (132c) are bent/shaped
relative to each other or otherwise shaped to be in tension when
assembled such that the tension applies a downward force on the
cooler (123).
Furthermore, FIG. 6 illustrates a stiffener member (130'') having a
planar frame portion (131) and extension tabs (132) having portions
(132d) and (132e), where the end portions (132d) extends over the
edge of the upper surface of the cooler (123). The portions (132d)
and (132e) are bent relative to each other or otherwise shaped to
be in tension when assembled such that end portion (132d) applies a
downward force on top surface of the cooler (123).
In the exemplary embodiments of FIGS. 4A, 5 and 6, the TIM layer
(127) between the cooler (123) and the chip (122) may be a
compliant filled adhesive or gel, or a soft solder layer such as
Indium, though other types of TIMs could also be used. Preferably,
a compliant thermal adhesive material or a soft solder material is
used to form the TIM1 layer (127) when there is a CTE mismatch
between the materials of the chip (122) (e.g., silicon) and the
metallic cooler (123) (e.g., copper) so as to maintain the
integrity of the thermal bond and counteract mechanical stresses
that may arise due to differential thermal expansion of the chip
and cooler surfaces. If the TIM1 layer (127) is formed of a low
strength material, or a if a gel-type TIM is used, the stiffener
extension tabs (132) can be sized and shaped to not only fixedly
hold the cooler (123) in position over the backside of the chip
(122), but to also apply a downward, compressive force to the
cooler (123) when assembled to the cooler (123), which clamps the
cooler (123) down against the backside surface of the chip (122).
This clamping force can prevent any large tensile force being
applied across the TIM1 layer (127) due to shock or vibration,
which could tear or separate the TIM layer (127) from the surfaces
to which it is bonded. This could be accomplished, for example, by
applying an appropriate weight to the top surface of the cooler
(123) when it is being attached to the stiffener extensions (132)
and the adhesive materials are being cured. The exemplary package
structures (100), (101) and (102) provide the high thermal
performance advantages of a lidless package (such as in FIG. 3)
i.e. only a single TIM layer (127) is provided in the thermal path
between the chip (122) and the cooler (123). Although no lid is
used, the chip is still protected by the copper cooler (123).
Further, a lower, and more repeatable, thermal resistance is
achieved with the TIM1 layer (127) when adhesive TIM materials are
used, the assembly process can be better controlled, and bond line
between the chip and cooler can be reduced when the cooler is
integrated into the first level package. Moreover, no attachment
holes are required in the mother board (110). Further, the
exemplary package structures (100), (101) and (102) allow for
uniformity of load distribution when LGA type connectors are used
to connect the module (120) to the board (110). With an LGA
connector, it is necessary to provide a uniform load to actuate the
LGA across the bottom surface of the package. The stiffener
extensions (130, 130', 130'') serve to couple the lid and stiffener
together, which makes it easier to provide such a uniform actuation
force. This is difficult to achieve with a lidless package such as
is shown in FIG. 3, as noted above.
Another advantage of the exemplary embodiments is that a smaller
metallic cooler can be used so the weight of the overall assembly
is minimized and the cooler size need not be any larger than is
required to effectively cool the chip. As noted above, the low
weight is important for BGA assembly, along with shock and
vibration resistance and it is desirable to minimize the cooler
size as the fabrication cost of coolers often scale with their size
and is significantly greater than that of stiffener, or lids. It is
to be further appreciated that the metallic stiffener with
extensions and cooler (123) function together to provide mechanical
rigidity to the flexible organic laminate chip carrier (121).
A number of assembly processes are possible, where it is
contemplated that in all cases that the cooler would be attached to
the 1.sup.st level package assembly before it is attached to a
mother board or node card. Such a sequence is highly desirable as
it allows an adhesive TIM (127) to be cured without subjecting the
mother board (110) to the additional processing step and also due
to logistical and yield issues. For the structures illustrated in
FIGS. 4 and 5, the cooler (123) could be attached after the chip
(122) and stiffener (130) are attached to the carrier (121). For
the structure in FIG. 6, the cooler (123) and stiffener (130'')
would need to be attached to the carrier and chip after the chip
was attached to the carrier.
In other exemplary embodiments of the invention, the metallic
cooler device can be mechanically coupled to the substrate carrier
using extension members that are integrally formed as part of the
cooler module, which are bonded to a separate stiffener member on
the substrate or directly to the substrate. For example, FIGS. 7, 8
and 9 are schematic cross section views of electronic modules
having metallic coolers with integrally formed extension elements
that are used to mechanically couple the cooler to the package.
FIG. 7 schematically illustrates an electronic module having a chip
level package with an integrated cooler module according to an
exemplary embodiment of the invention. In particular, FIG. 7 is a
schematic view of an electronic module (200) comprising a circuit
board (110) (or node card, printed wiring board, or printed circuit
card, etc,) and a chip package structure (220) mounted on the
circuit board (110). The module (200) is similar in structure to
previously discussed embodiments, except that the chip package
structure (220) includes a metallic liquid cooling module (223) (or
cooling apparatus or device) having integrally formed extensions
(240) which are coupled to a stiffener member (230). The stiffener
member (230) is a planar frame structure that is bonded to a
peripheral surface region of the substrate (121) using a layer of
adhesive material (233). The cooler extensions (240) extend from
the bottom sidewall surfaces of the cooler (223) and are bonded to
the stiffener member (230) using a layer of adhesive material
(234). In the exemplary embodiment of FIG. 7, the stiffener (230)
can be sized and shaped to provide sufficient bonding and rigidity
to the substrate (121) and the cooler extensions (240) can be sized
and shaped to provide adequate overlap of the stiffener member
(230) to adhesively bond the cooler extensions sufficiently to the
stiffener member (230).
FIG. 8 illustrates an electronic module (201) according to another
exemplary embodiment of the invention which is similar to the
module (200) of FIG. 7, except that the stiffener member (230') is
smaller and the cooler (223) includes longer extensions (241) that
extend from the bottom sidewall surfaces of the cooler (223) to the
edges of the stiffener (230') and carrier (121). In this exemplary
embodiment, the smaller footprint of the stiffener (230') provides
more surface area on the substrate (121) to mount components (128)
next to the chip (122), while ensuring that the overlap between the
cooler extensions (241) and the stiffener member (230') is
sufficient to adequately bond the cooler and stiffener.
FIG. 9 illustrates an electronic module (202) according to another
exemplary embodiment of the invention which is similar to the
exemplary embodiment of FIGS. 7 and 8, except that the metallic
cooler (223) includes extensions (242) that are directly bonded to
the peripheral surface region of the substrate (121). In
particular, in FIG. 9, the extensions (242) are not bonded to
separately formed and mounted stiffener member (as in FIGS. 7 and
8), rather, the extensions (242) are designed to have protruding
peripheral rim portion (242a) on a bottom surface thereof, which is
directly bonded to the substrate (121) using a layer of adhesive
material (233).
In the exemplary embodiments of FIGS. 7, 8 and 9, the cooler
extensions can be designed as continuous solid members (e.g., solid
plate) that extend from the bottom surface of the cooler (223) that
thermally bonds to the backside of the chip (122). In other
exemplary embodiments, the extensions can be formed with apertures
(similar in concept to the apertures of the stiffener extension
tabs of FIG. 4B) as desired to reduce the amount of stress that
would be imparted to the organic carrier substrate (121) and the
chip (122). The portions of the cooler extensions adjacent the
cooler (223) could have a thickness in the range of 0.5 to 2 mm if
it is continuous and solid between the cooler (223) and where the
extensions overlap the stiffener or reach the edge of the carrier.
The embodiment shown in FIGS. 7, 8 and 9 would allow the use of an
LGA connector as the cooler extensions would couple a load from the
cooler into the stiffener, or directly into the organic carrier
(121) and would be light enough for BGA reflow.
In other exemplary embodiments of the invention, a metallic cooler
device can be mechanically coupled to a first level chip package
substrate by bonding the sidewalls of a cooler to edges of an
opening which is formed in a package lid, where the lid is either
attached to a stiffener which is attached to the carrier, or where
the lid is attached directly to the carrier, such as illustrated in
the exemplary embodiments of FIGS. 10A/10B and 11. In particular,
FIGS. 10A and 10B are schematic views of an electronic module (300)
comprising a circuit board (110) (e.g., PCB, node card, printed
wiring board, printed circuit card, etc,) and a chip package
structure (320) mounted on the circuit board (110). FIG. 10A is a
schematic side view of the electronic module (300) and FIG. 10B is
a top plan view of the electronic module (300) along line 10B-10B
in FIG. 10A. The electronic module (300) is similar in structure to
previously discussed embodiments, except that the chip package
structure (320) includes a planar package lid (340) having an
aperture formed in a central region thereof, wherein the metallic
liquid cooling module (123) is disposed in the aperture formed in
the planar package lid (340). The edges of the metallic cooler are
joined to an opening which is formed in a central region of the
package lid (340) and where the lid (340) is adhesively attached to
a stiffener member (330). The cooler device (123) is bonded to the
inner edges of the lid aperture using a bond material (335), the
package lid (340) is adhesively bonded to the stiffener member
(330) via a layer of adhesive (334) and the stiffener (330) is
bonded to the peripheral surface region of the substrate (121) with
a layer of adhesive material (333). In FIG. 10A, an excess material
of the TIM (127) between the chip (122) and the cooler (123) can be
used to form a bridging bond (129) in the gap between the
cooler/lid edge and the carrier surface (121) or underfill (126)
adjacent to the sides of the chip (122). If an adhesive material is
used for the TIM (127), the bridging bond (129) between the
cooler/lid and the surface of the carrier in the region near the
chip provides further means to prevent chip warpage. It is to be
understood that the bridging bond (129) can be implemented in other
exemplary embodiments described above.
FIG. 10B is a schematic top view of the package shown in FIG. 10A,
including the fluid inlet and outlet ports (P1 and P2). The join
between the cooler and the lid is also indicated. As with previous
embodiments, the attachment between the cooler and the lid would
couple them together and enable the use of an LGA connector.
FIG. 11 is a cross-sectional view of an electronic module (301)
according to another exemplary embodiment of the invention, which
is similar to the embodiment of FIG. 10A, except that the package
lid (340) includes a peripheral rim portion (341a) that is formed
on a peripheral bottom surface of the lid (340), which is directly
bonded to the peripheral surface region of the substrate (121)
using adhesion layer (333). Note that the lid serves to flatten and
increase the stiffness of the laminate carrier when no stiffener is
used. FIG. 11 differs from FIG. 10 in that the separate stiffener
member (330) in FIG. 10 is eliminated.
In the exemplary embodiments of FIGS. 10 and 11, the package lid
(340) can be formed of copper by stamping, coining or machining a
bulk block of copper, wherein the lid aperture can be readily
fabricated by these methods. The thickness of the lid may be 0.5 to
2.0 mm thick. The copper lids can be plated with nickel, or nickel
and gold. The package lid (340) and the cooler (123) may be bonded
using a layer of bond material (335), which can be solder, or a
suitable adhesive material that could vary between a low modulus,
flexible adhesive to a high strength structural adhesive to control
the mechanical interaction of the cooling structure with various
chip/substrate structures. The cooler size is minimized and the
cooler (123) does not need to be any larger than is required to
effectively cool the chip.
The exemplary package structures of FIGS. 10 and 11 can be
assembled various ways. The cooler (123) and lid (340) could be
assembled to the carrier (121) and chip (122) by either lid first,
cooler first, or both at the same time after joining them together,
or both at the same time and joined them together at the same time
or later. In one preferred process, the cooler (123) and lid (340)
may be joined as a subassembly, and then attached to the chip (122)
and carrier (121) to minimize handling of individual parts during
module assembly processing.
FIGS. 12A and 12B schematically illustrate a metallic liquid cooler
device according to an exemplary embodiment of the invention. FIGS.
12A and 12B illustrate an exemplary framework of a metallic liquid
cooler device (400) that may be implemented as the liquid cooler
devices (123) and (223) shown in the exemplary package structures
described above. FIG. 12A is a schematic cross sectional view of a
metallic cooler device (400) taken along line 12A-12A in FIG. 12B
and FIG. 12B is a schematic top plan view of the metallic cooler
device (400) from the perspective of line 12B-12B in FIG. 12A.
In general, the liquid cooler device (400) includes a cooler body
(404) comprising a plurality of thermal fins (401) and flow
channels (402), and a cover plate (403). It is to be understood
that other configurations of thermal fins and flow channels can be
used such as mesh structures or staggered stacked microchannels as
described in U.S. application Ser. No. 12/120,069, filed May 13,
2008, which is commonly assigned and incorporated herein by
reference. The cover plate (403) is bonded to the top surface of
the body (404) and the tops of the fins (401) thereby defining a
chamber for the flow of a coolant (e.g., water) through the
channels (402) between the inlet and outlet manifolds M1, M2. Heat
removal is achieved by thermal contact between the fins (401) and
the coolant fluid that flows through the channels (402). As shown
in FIG. 12B, the thermal fins (401) include a plurality of
elongated, parallel thermal fins that may be formed by
etching/machining a block of metallic material (e.g., copper) to
form the cooler body (404) flow channels (402) and tapered manifold
channels (M1) and (M2). In the exemplary embodiment, the manifold
channel Ml is a coolant supply manifold and the manifold channel M2
is a coolant return manifold, arranged on opposite ends of the flow
channels (402). Further, the dotted circles P1 and P2 represent
where respective input and output ports would be made in the cover
plate (403) to provide the fluid supply/return connections.
The input manifold M1 and output manifold M2 are formed with
tapered cross section channels to maintain the velocity of the
fluid flow near constant and reduce dynamic pressure drop. For
instance, the cross-sectional area of the flow channel of the
supply manifold (M1) that is aligned with the inlet port (P1) is
tapered to provide uniform distribution of coolant fluid to the
input ends of the flow channels (402) fed by coolant fluid from the
input manifold M1. Moreover, the cross-sectional area of the flow
channel of the return manifold (M2) that is aligned with the output
port (P2) is tapered to provide uniform redistribution of the
output coolant fluid that flows out from the ends of each flow
channel (402) into the output manifold M2. In such framework, the
area of the flow channels of the manifolds are tapered sufficiently
to reduce the dynamic pressure drop by maintaining the velocity of
the coolant fluid substantially, or very close to, constant among
the flow channels (402) in the metallic cooler device (400).
FIGS. 12A and 12B further illustrate that the outer perimeter walls
of the cooler device (400) have a perimeter seal surface area (or
seal band), of at least width W.sub.P around the outside perimeter
of the cooler. The perimeter seal width W.sub.P is typically in the
range of 0.2 to 2.0 mm, to provide sufficient bonding area for
bonding the cover plate (403) to the cooler body (404). An active
cooling area of the cooler (400) is illustrated in FIG. 12B as a
region with area of L.sub.AA.times.W.sub.AA which includes the
alternating thermal fins (401) and flow channels (402) (or other
microstructures which have a reduced hydraulic diameter and
increased cooler surface area). The perimeter seal areas W.sub.P
and manifold regions M1, M2 are not considered to be part of the
active cooling area of the cooler (400). The cooler (400) has a
base thickness (T.sub.B), typically in the range of 0.3 to 2.4 mm,
of solid material under the active cooling area
L.sub.AA.times.W.sub.AA, as indicated in FIG. 12A.
When constructing chip package structures with integrated metallic
coolers according to exemplary embodiments of the invention as
described herein, it is preferable to minimize the size of metallic
cooler device while achieving sufficient cooling performance. For
instance, with regard to cooler weight, if a BGA attachment to the
board is used, it is desirable to minimize the total weight of the
1.sup.st level package assembly. For a 50.times.50 mm carrier,
increasing the Cu lid thickness from 2 mm to 3 mm was found to
result in an increase in shorting between the BGA balls unless a
modified join process with tighter process controls was used.
Copper has a density of about 8.96 grams per cubic centimeter, so a
3 mm thick Cu lid corresponds to a weight of about 2.7 grams per
square centimeter of carrier area. Therefore, an exemplary factor
to consider when designing package structures is that the weight of
the package lid, cooler, and stiffener should be less than the
weight of a 3 mm thick Cu layer equal in dimensions to the carrier
size, i.e. less than 2.7 grams per square cm of carrier area. The
weight scales with the carrier size as proportionately more solder
balls are used on a larger carrier.
Further, various factors may be considered when constructing
metallic cooler devices that are thermally bonded directly to the
backside of flip chip mounted chips on a flexible substrate so that
the active region of the cooler is smaller than the area of the
chip, but including the seal regions and manifold regions, the
cooler is equal in size, or extends beyond the chip. With current
200 mm and 300 mm diameter silicon wafers, unless thinned, the
resulting integrated circuit chips are about 0.7 to 0.8 mm thick.
For a typical chip, the footprint of the active (powered) area
extends to within about 0.1 mm to 0.2 mm from the physical edge of
the chip. Given the thickness of the chip and the small distance
from the active powered area to the chip edge, heat will spread
over the entire chip area. In this regard, the entire chip may be
considered to be powered and just the diced chip size considered,
as long as the entire chip is in thermal contact with the cooler.
As will be explained below, in one exemplary preferred embodiment
of the invention, when a manifold region is not present between the
active area and the perimeter seal band, the preferred
configuration is for the cooler active area to be somewhat smaller
than the chip size and for the perimeter seal to extend beyond the
end of the chip.
For instance, FIG. 13 illustrates an exemplary cooler device (400')
that is thermally bonded to the backside of the chip (122) using
thermal TIM layer (127) (as discussed above). In FIG. 13, the
cooler (400') is sized such that the cooler width is similar to the
width Wc of the chip (122) where the sides of the cooler (400) do
not extend past the sides of the chip (122). FIG. 14 illustrates an
exemplary cooler device (400'') that is thermally bonded to the
backside of the chip (122) using thermal TIM layer (127) (as
discussed above), where the cooler (400'') is sized such that the
cooler width is greater than the width Wc of the chip (122) where
the sides of the cooler (400'') extend past the sides of the chip
(122). The active area of the cooler (400') in FIG. 13 is smaller
than the active area of the cooler (400'') of FIG. 14 at least with
regard to the difference in the widths W.sub.AA of the respective
active areas. However, as will be shown below, the reduced active
area (in FIG. 13) has little or no effect on the thermal
performance. Given that the fabrication cost of a cooler is greater
per unit area than that of a lid, stiffener extensions, etc . . . ,
it is desirable to minimize the cooler size, and hence active
area.
Thermal modeling was performed using commercially available
software to determine optimum and minimum practical sizes for the
"active cooler area" of a metallic cooler with a fixed coolant
flow. In one process, a model of a package structure was defined
with a silicon chip thermally bonded to a copper cooler device
using a thin TIM layer. In the model, the silicon chip was defined
to have a fixed size (area) of 22.times.22 mm, and a thickness of
0.785 mm. The TIM layer was defined to have a thermal conductivity
of 3.8 W/m-K and a thickness of 2 mil. An effective heat transfer
coefficient, determined assuming constant total liquid flow, was
applied on the cooler active area along the cooler base and top,
and the effects of the water temperature rise were considered. It
was assumed that the fluid inlet was along a line dividing the chip
in half, the outlets were parallel and at the edges of the active
cooler area, and that the inlet and outlet regions did not displace
any fins. The cooler base thickness, active area size, and
perimeter seal width were varied. It was assumed that the cooler
was fabricated from copper and that the sides of the cooler, i.e.
the width of the perimeter seal, extended to a cooler top surface
which had a thickness equal to the cooler base thickness and the
cooler top was attached to the active cooling structure as was the
cooler base. The total thermal resistance was calculated by
dividing the difference between the maximum temperature on the
active side of the chip and the inlet water temperature by the
total power. A uniform power distribution across the chip, and a
square cooler with a uniform seal width on all sides was assumed
with no manifold regions. In the modeling, it was also assumed that
the cooler base was flat and coplanar under both the active cooled
region and the seal regions.
FIGS. 15A.about.15D are exemplary graphical diagrams that
illustrate results of thermal modeling based on the above mentioned
parameters. In particular, FIGS. 15A, 15B, 15C and 15D graphically
illustrate a total thermal resistance (Rtotal) versus active cooler
width W.sub.AA (in mm) for coolers with seal band widths Wp of 0.2,
0.5, 1.0 and 2.0 mm with fixed base thickness Tb values of 0.3 mm
(FIG. 15A), 0.6 mm (FIG. 15B), 1.2 mm (FIG. 15C), and 2.4 mm (FIG.
15D). As shown in FIG. 15A, for a seal band width Wp of 2 mm, the
total thermal resistance was nearly constant for active cooler
widths W.sub.AA between 20 and 22.5 mm (i.e. within a few percent
of the minimum value). Moreover, FIGS. 15B.about.15D illustrate
that as the cooler base thickness Tb is increased, the minimum
value for a fixed seal band width Wp increases slightly, due to the
temperature drop in the thicker copper base. With a 2 mm seal band,
in all cases, reducing the active area to 20 mm resulted in an
increase in the thermal resistance by a maximum of 2% from the
minimum value and in most cases by less.
For the case of a 1 mm seal band width Wp, the thermal resistance
is shown to be nearly constant, or slightly increase, when the
active area is reduced to 20.5 mm. When the active cooled area is
less than 20 mm wide, the thermal resistance is shown to increase
sharply as the seal band region does not extend to the edge of the
chip. The total thermal resistance slowly increases for active
areas greater than about 22 mm because the average fluid velocity
inside the cooler active volume decreases hence reducing the local
heat transfer coefficient between the fluid and the microstructure
inside the cooler. The performance is found to be further reduced
by increasing the amount of coolant bypassing the chip along the
sides of the cooler and which is heated to a lesser degree than
coolant which passes directly over the chip. Similar trends can be
observed for the 0.5 mm and 0.2 mm seal band results. When no
manifold region is present, or along the sides of the cooler
without manifold regions, the active cooler size is preferably
smaller than the chip size but the active cooler width plus the
seal band widths is preferable equal to or somewhat greater than
the chip size.
The above discussion suggests that a minimum base thickness is
desirable, but the modeling results in FIGS. 15A.about.15D do not
consider cooler devices having manifold regions at opposite ends of
the active region before the perimeter seal region is reached (as
in FIG. 12B) Depending on the cooler framework, such manifold
regions may, or may not, be necessary. If manifold regions are
present at the end of the active regions before the perimeter seal,
then the width of the manifold region between the active region and
the perimeter seal is preferably less than one to two times the
base thickness of the cooler (e.g. if the base is 0.5 mm thick, the
manifold region should be no more than 1 mm wide). Such a
relationship allows heat spreading in the base to provide adequate
cooling under the manifold region and would permit the active area
of the cooler to be smaller than the chip area. An alternate
solution would be to have the active area of the cooler be smaller
than the cooler in the direction perpendicular to the coolant flow
direction to reduce cooler size and cost, but be nearly equal, or
equal to, the chip size in the direction parallel to the coolant
flow.
Although illustrative embodiments have been described herein with
reference to the accompanying drawings, it is to be understood that
the present system and method is not limited to those precise
embodiments, and that various other changes and modifications may
be affected therein by one skilled in the art without departing
from the scope or spirit of the invention. All such changes and
modifications are intended to be included within the scope of the
invention as defined by the appended claims.
* * * * *